1. Field of the Invention
The present invention pertains to railroad ties for use in laying track for railroad use.
2. Background Art
Railroad ties are used in enormous numbers each year. The ties support and position the track upon which railroad equipment rides, and distribute the load of the train onto the roadbed as well. The roadbed is generally formed of very coarse crushed stone. Most railroad ties are prepared from lumber. Because of the relatively large size of the ties, i.e. 6xe2x80x3 (15 cm) by 8xe2x80x3 (20 cm) by 8 feet (2.4 m), an enormous number of board feet of virgin lumber is consumed each year. The ties are generally preservative impregnated, i.e. with creosote and/or synthetic chemical preservatives.
Proposals to alter the nature of ties and thus limit the use of virgin lumber have been legion. For example, it has been proposed to manufacture ties from wood particles which may be obtained from smaller, more easily replaceable trees, or as scrap from the wood processing industry. However, the resulting ties do not have the strength or weatherability characteristics of wood, and may also vary in their spike holding capability. To improve upon these properties, it has been proposed in U.S. Pat. No. 4,202,494 to encase the exterior of the tie with polypropylene by injection molding the latter around the tie. However, the injection molding process for items the size of ties involves exceptionally heavy tonnage molding presses, which is capital intensive. Moreover, while the polypropylene sheath assists in minimizing water uptake, it adds little to the strength characteristics, and in cold weather or after extensive exposure to sunlight, may become brittle and crack, particularly while spike driving. Finally, the sheath also traps water within the tie, increasing susceptibility to rotting.
It has also been proposed to recycle railroad ties, thus prolonging their useful life. In U.S. Pat. No. 4,286,753, for example, railroad ties are sawn in pieces and composite wood portions adhesively bonded thereto, either on the exterior, the interior, or both. The refurbished ties have a combination of the advantages and disadvantages of both conventional wood ties and composite ties.
Associated with railroad trackage is the need to provide numerous electrical power sources and signaling means, for example to operate switches, semaphores, signal lights, railroad crossing lights, etc. In the past, the cabling necessary for power or communication has been encased in metal conduit and positioned over the roadbed ballast or within it. The conduit and cabling it contains may be subject to damage during construction and repair of the roadbed. When exposed or shallowly buried, it is subject to heaval by frost, and snagging by materials which inadvertently dangle from the train. The loss of signal capability may be extremely dangerous. For example, railroad crossings may be without warning means to notify motorists that a train is approaching.
It would be desirable to provide railroad tie products which minimize the use of virgin lumber. It would be further desirable to provide a composite tie which exhibits enhanced weatherability while maintaining strength characteristics and the ability to position and support rails with conventional spikes and plates. It would further be desirable to provide a means of cabling which minimizes the opportunity for damage to the cabling.
The present invention pertains to composite railroad ties having a core, preferably of a wood substance, the core having been wrapped around its exterior with a reinforcing fiber xe2x80x9coverwrapxe2x80x9d impregnated with a curable matrix composition which is subsequently cured. The core of the composite tie may comprise recycled railroad ties, or a molded composite material, and may be configured to contain one or a plurality of cable conduits. Surprisingly, spikeability and spike retention are improved over that of conventional ties. The invention further pertains to composite ties manufactured to include integral conduit.